Lesson 6 – Centre of Mass & System of Particles
Objective Questions – Set 6
(Final Refinement · IIT-Advanced Logic)
This is the final objective set. It focuses on law recognition, calm elimination, and time efficiency.
Q1. (Statement Based MCQ)
Consider the following statements about centre of mass:
S1: COM velocity remains constant if net external force is zero.
S2: COM acceleration can be non-zero even if momentum is zero.
S3: COM path depends on internal forces.
S4: COM acceleration is same in all inertial frames.
Which statements are correct?
A) S1, S2, S4
B) S1, S3
C) S2, S3, S4
D) S1, S4
Correct Answer: A
Q2. (IIT-JEE Advanced | Integer Type)
A system of mass 12 kg is acted upon by a constant external force. The centre of mass acceleration is 2 m/s². Find the magnitude of the external force (N).
F = M a = 12 × 2 = 24
Answer: 24
Q3. (Conceptual MCQ)
A system of particles is isolated. Which of the following quantities must be zero?
A) Acceleration of centre of mass
B) Velocity of centre of mass
C) Momentum of each particle
D) Kinetic energy of system
Correct Answer: A
Q4. (Advanced MCQ · Frame Logic)
A system is observed from two different inertial frames. Which quantity remains the same in both frames?
A) Velocity of centre of mass
B) Momentum of centre of mass
C) Acceleration of centre of mass
D) Kinetic energy of system
Correct Answer: C
Q5. (IIT-JEE Advanced | Numerical Logic)
An isolated system initially at rest explodes into fragments. One fragment has kinetic energy 50 J. Find the kinetic energy of centre of mass (J).
COM velocity remains zero.
Answer: 0
Q6. (Multiple Correct)
Which statements are always true?
A) COM motion depends on external forces only
B) Internal forces can change COM velocity
C) COM can lie outside the physical body
D) COM velocity is frame dependent
Correct Answers: A, C, D
Q7. (One-Line Advanced)
Which single equation completely governs the motion of centre of mass in an inertial frame?
A) ΣF = ma
B) ΣFexternal = M acm
C) Σp = constant
D) Work–Energy theorem
Correct Answer: B
Q8. (Advanced Concept)
A system has constant velocity of centre of mass. Which of the following may still change?
A) Momentum of system
B) Acceleration of COM
C) Relative velocities of particles
D) Net external force
Correct Answer: C
Q9. (Trap MCQ)
Zero external force implies:
A) Zero velocity of COM
B) Zero momentum at all times
C) Constant velocity of COM
D) Zero internal forces
Correct Answer: C
Q10. (Final Polisher)
Why is centre of mass concept powerful in multi-particle systems?
A) It removes internal forces from analysis
B) It avoids Newton’s laws
C) It eliminates energy conservation
D) It gives exact particle paths
Correct Answer: A
OBJ–6 FINAL EXAM TIPS
✔ Acceleration depends on force, not momentum
✔ Frame matters for velocity, not acceleration
✔ Explosion → KE changes, COM motion doesn’t
✔ Never assume COM lies inside body
✔ Law first, option later
📘 Centre of Mass & System of Particles – Complete Physics Library
This library is a complete learning package for Intermediate + IIT JEE Physics covering Centre of Mass and System of Particles.
It includes theory, solved examples, objective questions, IIT-level problems, revision strategies, tricks, and exam-oriented guidance.
📂 Stage 1: Intermediate Complete Notes (Concept Foundation)
📂 Stage 2: Advanced Concepts & Applications
📂 Stage 3: Objective Questions, Tough Problems & Revision
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Vision: Concept clarity • Logical thinking • Exam excellence
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